1. Field of the Invention
The present invention relates to a semiconductor circuit, and in particular to a semiconductor circuit having an operational amplifier.
2. Description of the Related Art
As circuits which control an input voltage and obtain a stabilized output voltage, there are known circuits such as a series regulator, a switching regulator, and a charge pump circuit. For example, JP 2007-159299A discloses a low voltage output regulator.
In a circuit such as a series regulator, there is used an operational amplifier which has an output voltage divided by resistor elements which form a negative feedback circuit and which has the divided voltage input as a feedback signal. More specifically, a reference voltage is connected to a first input terminal of the operational amplifier, and a second input terminal is connected to resister elements which divide the output voltage of the operational amplifier. Here, in order to change the resistance values of the resistor elements so as to adjust the output voltage of the operational amplifier, an external resistor element may be mounted outside of the circuit having the operational amplifier.
When the semiconductor circuit and the external resistor elements described above are mounted on a printed circuit board, if the electrical connection is lost, such as by detachment of the external resistor element, the negative feedback circuit of the operational amplifier is disconnected. When this occurs, the operational amplifier functions as a comparator, the output voltage becomes higher than the voltage during normal operation, and an excessive voltage may be applied to an external load which is connected to the output terminal of the operational amplifier (comparator)